1. Field of the Invention
The invention concerns a monolithic integrated optical semiconductor component and a process for fabricating an optical semiconductor device.
2. Description of the Related Art
Such a semiconductor component is used for producing, regenerating and processing signals, or for switching signals in optical communications, particularly in optical transmission networks which operate mostly without any optoelectronic signal conversion. To that end active waveguide regions are monolithically integrated in the semiconductor component, such as e.g. lasers, switches, modulators, amplifiers or detectors with passive waveguide regions, such as e.g. passive optical waveguides, branching points, filters or couplers.
A laser with a buried ridge stripe waveguide, which is monolithically integrated with a passive waveguide, is known from an article by D. Remiens et al ("Buried Ridge Stripe Lasers Monolithically Integrated with Butt-Coupled Passive Waveguides for OEIC", SPIE, Vol. 1362, pages 323-330). The passive waveguide is also a buried ridge stripe waveguide which is covered by a p-doped cap layer. However high absorption losses in the passive waveguide are a disadvantage. In addition the laser is manufactured in accordance with a process comprising several steps which require the laser to be precisely aligned with lithographic masks.
Furthermore a monolithic integrated optical semiconductor component with active and passive waveguide regions is known from the publication of the European patent application EP 616 243 A from which U.S. patent applications having Ser. Nos. 08/198,830 filed Feb. 18, 1994 and 08/474,686 filed Jun. 7, 1995 claim priority. It describes a cascaded optical space switch which has a ridge stripe waveguide in both the active as well as the passive waveguide regions. Furthermore a process is indicated whereby this ridge stripe waveguide can be applied in a single coating process. A cap layer is not described in EP 616 243 A.
In many state of the art applications the monolithic integrated optical semiconductor components preferably use buried ridge stripe waveguides in the active waveguide regions. As is known e.g. from U. Koren et al, "Semi-Insulating Blocked Planar BH GaInAsP/InP Laser with High Power and High Modulation Bandwidth", Electr. Letters, Vol. 24, No. 3, 4th Feb. 1988, this waveguide structure is suitable above all for lasers because of the low threshold current, the achievable high output and the long service life, but it is also used for integrated amplifiers and switches. In contrast, as is known e.g. from T. Koch et al, "Semiconductor Photonic Integrated Circuits", IEEE J. Quant. Electr., Vol. 27, No. 3, 1991, the use of rib waveguides is preferred in the passive waveguide regions due to their low absorption losses. But the integration of different optical waveguide structures leads to technologically expensive manufacturing processes, and additional leakage losses and reflections occur in the junctions between the active and the passive waveguide regions having different waveguide structures.